Copolymer useful as a pour point depressant for a lubricating oil

Abstract: There is provided a copolymer useful as a pour point depressant for hydrocarbon lubricating oils, and a method of making such copolymer. The copolymer comprises from about 15 mole percent to about 67 mole percent comonomeric units derived from one or more (C₈-C₁₅) alkyl (meth)acrylate monomer, from about 3 mole percent to about 40 mole percent comonomeric units derived from one or more (C₁₆-C₂₄) alkyl (meth)acrylate monomer, and from greater than 30 mole percent to about 65 mole percent comonomeric units derived from one or more (C₁-C₄)alkyl (meth)acrylate monomer.

Description: The present invention is concerned with certain alkyl (meth)acrylate copolymers and their use as additives for lowering the pour point of hydrocarbon lubricating oils. Lubricating base oils, e.g., commercial petroleum distillate oils, commonly contain paraffinic hydrocarbons that crystallize upon cooling thereby significantly increasing the viscosity of the oil. At a sufficiently low temperature, the crystalline wax structure ultimately causes gelation of the base oil. The low temperature fluidity of petroleum distillate oils can be improved by dewaxing and such oils are typically dewaxed to a pour point, i.e., the lowest temperature at which the oil remains fluid, of about -15°C. Further lowering of the pour point is typically achieved by the use of a pour point lowering additive, i.e., a "pour point depressant", that further lowers the pour point of the dewaxed oil, typically down to about -30°C. The composition of petroleum distillate oils is variable and the relationship between base oil composition and the composition of those additives effective in lowering the pour point of any particular base oil is often poorly characterized. It is, therefore, not always possible to reliably prescribe a particular pour point depressant composition for effectively treating a particular base oil, i.e., treatment of any particular oil with pour point depressant remains, to a large extent, an empirical undertaking. Poly(alkyl methacrylate) pour point depressants comprising higher alkyl esters, e.g., those including 12 or more carbon atoms per alkyl group, are known. It is believed that the elongated paraffin-like alkyl portions of such pour point depressants are incorporated into the growing paraffin crystals, thereby inhibiting further crystal growth and preventing formation of an extensive interlocking paraffin crystal structure. In US-A-4,867,894, Pennewiss et al disclose a poly(alkyl methacrylate) pour point depressant wherein from 10 to 30, preferably 10 to 20, mole percent methyl methacrylate is copolymerized with alkylmethacrylate monomers having relatively long, i.e., C 16 and higher, alkyl groups to form a pour point depressant additive. Pennewiss et al teach that such an additive has a lower cost due to substitution of relatively low cost methyl methacrylate for a portion of relatively high cost higher alkyl esters and that, within the disclosed ranges of methyl methacrylate mole percent, such a substitution does not diminish the effectiveness of the additive as a pour point depressant. WO 89/01507 discloses certain poly(methacrylate) polymers which are useful as pour point depressants for lubricating oils, the polymers having methacrylate repeating units wherein the average chain length of the alkyl group in the methacrylate repeating units is 12.6 to 13.50. However, WO 89/01507 does not disclose or teach the specific copolymers with which the present invention is concerned. There is a constant effort in the art to provide pour point depressants that provide cost effective performance in a wide range of lubricating oil base stocks. We have now found a copolymer which provides high performance as a pour point lowering additive in a wide range of lubricating oil base stocks at a reduced cost. According to the present invention there is provided a random copolymer, which comprises: i) from 15 mole percent to 67 mole percent first repeating units, wherein each of the first repeating units has the structural formula: wherein each occurrence of R 1 is independently H or methyl, and each occurrence of R 2 is independently selected from the group consisting of (C 8 -C 15 )alkyl; ii) from 3 mole percent to 40 mole percent second repeating units, wherein each of the second repeating units have the structural formula: wherein each occurrence of R 3 is independently H or methyl, and each occurrence of R 4 is independently selected from the group consisting of (C 16 -C 24 ) alkyl; and iii) from greater than 30 percent to 65 mole percent third repeating units, wherein each of the third repeating units have the structural formula: wherein each occurrence of R 5 is independently H or methyl, and each occurrence of R 6 is independently selected from the group consisting of (C 1 -C 4 )alkyl. According to the present invention there is also provided a method for making a copolymer according to the invention and which is useful in lowering the pour point of a lubricating oil. The method comprises copolymerizing a mixture of monomers in a hydrocarbon diluent, wherein the monomer mixture comprises from 15 mole percent to 67 mole percent of one or more (C 8 -C 15 )alkyl (meth)acrylate monomer, from 3 mole percent to 40 mole percent of one or more (C 16 -C 24 )alkyl (meth)acrylate monomer, and from greater than 30 mole percent to 65 mole percent, of one or more (C 1 -C 4 )alkyl (meth)acrylate monomer. The present invention further provides a pour point depressant composition, which comprises about 100 parts by weight of a copolymer according to the present invention, or of a copolymer prepared by the method of the present invention, and from 15 to 600 parts by weight of a hydrocarbon diluent. The present invention still further provides a method for lowering the pour point of a lubricating oil base stock, which comprises adding to the base stock from 0.05 weight percent to 1.0 weight percent, based on the weight of lubricating oil base stock, of a copolymer according to the present invention, or of a copolymer prepared by the method of the present invention. The present invention still further provides a lubricating oil composition, which comprises a lubricating oil base stock and from 0.05 weight percent to 1.0 weight percent, based on the weight of lubricating oil base stock, of a copolymer according to the present invention, or of a copolymer prepared by the method of the present invention. The random copolymer of the present invention includes from 15 mole percent to 67 mole percent first repeating units, each having the structural formula (1): wherein each occurrence of R 1 is independently H or methyl, and each occurrence of R 2 is independently selected from the group consisting of (C 8 -C 15 )alkyl. Preferably, R 1 is methyl. As used herein, (C 8 -C 15 ) alkyl means any straight or branched alkyl group having 8 to 15 carbon atoms per group, e.g., octyl, nonyl, decyl, isodecyl, undecyl, lauryl, tridecyl, myristyl or pentadecyl. Preferably, R 2 is(C 10 -C 15 )alkyl . More preferably, R 2 is selected from the group consisting of isodecyl, lauryl, tridecyl, myristyl, pentadecyl and mixtures thereof, and even more preferably R 2 is selected from the group consisting of lauryl, tridecyl, myristyl, pentadecyl and mixtures thereof. Preferably, the copolymer includes from 25 mole percent to 60 mole percent first repeating units. More preferably, the copolymer includes from 25 mole percent to 40 mole percent first repeating units. The copolymer includes from 3 mole percent to 40 mole percent second repeating units, each having the structural formula (2): wherein each occurrence of R 3 is independently H or methyl, and each occurrence of R 4 is independently selected from the group consisting of (C 16 -C 24 ) alkyl. Preferably, R 3 is methyl. As used herein, (C 16 -C 24 ) alkyl means any straight or branched alkyl group having 16 to 24 carbon atoms per group, e.g., stearyl, cetyl, heptadecyl, nonadecyl or eicosyl. Preferably, R 4 is (C 16 -C 20 ) alkyl. More preferably, R 4 is selected from the group consisting of stearyl, cetyl, eicosyl and mixtures thereof. Preferably, the copolymer includes from 10 mole percent to 35 mole percent second repeating units. More preferably, the copolymer includes from 15 mole percent to 30 mole percent second repeating units. The copolymer includes from greater than 30 mole percent to 65 mole percent third repeating units, each having the structural formula (3): wherein each occurrence of R 5 is independently H or methyl, and each occurrence of R 6 is independently selected from the group consisting of (C 1 -C 4 )alkyl. Preferably, R 5 is methyl. As used herein, (C 1 -C 4 )alkyl means any straight or branched alkyl group having 1 to 4 carbon atoms per group, e.g., methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or t-butyl. Preferably, R 6 is selected from the group consisting of methyl, n-butyl, isobutyl and mixtures thereof. Most preferably, R 6 is methyl. Preferably, the copolymer includes from 32 mole percent to 50 mole percent third repeating units. More preferably, the copolymer includes from 35 mole percent to 45 mole percent third repeating units. Preferably, in the copolymer according to the present invention, R 1 , R 3 and R 5 are each methyl. The copolymer of the present invention preferably has a number average molecular weight, determined, e.g., by gel permeation chromatography, from 20,000 to 80,000, preferably from 25,000 to 70,000, and most preferably from 28,000 to 60,000 . The copolymer of the present invention preferably has a weight average molecular weight, determined, e.g., by gel permeation chromatography, from 50,000 to 200,000, preferably from 50,000 to 175,000, and most preferably from 50,000 to 100,000. The copolymer of the present invention can be made by free radical initiated polymerization of alkyl (meth)acrylate monomers. The terminology "(meth)acrylate" is used herein to generally refer to acrylate esters, methacrylate esters and mixtures thereof. Commercially available alkyl (meth)acrylate monomers may be, and typically are, mixtures of esters. Such mixtures are typically referred to, and are referred to herein, using a contracted version of the names of the ester species predominating in the mixture, e.g., "lauryl-myristyl methacrylate", "cetyl-eicosyl methacrylate", "cetyl-stearyl methacrylate" and "dodecyl-pentadecyl methacrylate". In a preferred embodiment, each of the first repeating units of the copolymer of the present invention is independently derived from a (C 8 -C 15 )alkyl methacrylate monomer, preferably a (C 10 -C 15 )alkyl methacrylate monomer. As used herein, "(C 8 -C 15 )alkyl methacrylate monomer" means an alkyl ester of methacrylic acid having a straight or branched alkyl group of 8 to 15 carbon atoms per group. Suitable (C 8 -C 15 ) alkyl methacrylate monomers include, e.g., octyl methacrylate, nonyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, myristyl methacrylate, pentadecyl methacrylate, and mixtures thereof. In a particularly preferred embodiment, each of the first repeating units of the copolymer of the present invention is independently derived from a monomer selected from the group consisting of isodecyl methacrylate, lauryl methacrylate, myristyl methacrylate, tridecyl methacrylate and pentadecyl methacrylate, e.g., lauryl-myristyl methacrylate or dodecyl-pentadecyl methacrylate. In a preferred embodiment, each of the second repeating units of the copolymer of the present invention is independently derived from a (C 16 -C 24 )alkyl methacrylate monomer, preferably a (C 16 -C 20 )alkyl methacrylate monomer. As used herein, "(C 16 -C 24 )alkyl methacrylate monomer" means an alkyl ester of methacrylic acid having a straight or branched alkyl group of 16 to 24 carbon atoms per group. Suitable (C 16 -C 24 ) alkyl methacrylate monomers include, e.g., stearyl methacrylate, cetyl methacrylate, heptadecyl methacrylate, nonadecyl methacrylate and eicosyl methacrylate. In a particularly preferred embodiment, each of the second repeating units of the copolymer of the present invention is independently derived from a monomer selected from the group consisting of stearyl methacrylate, cetyl methacrylate and eicosyl methacrylate, e.g., cetyl-stearyl methacrylate or cetyl-eicosyl methacrylate. In a preferred embodiment, each of the third repeating units of the copolymer of the present invention is independently derived from a (C 1 -C 4 )alkyl methacrylate monomer. As used herein, "(C 1 -C 4 )alkyl methacrylate monomer" means an alkyl ester of methacrylic acid having a straight or branched alkyl group of 1 to 4 carbon atoms per group. Suitable (C 1 -C 4 ) alkyl methacrylate monomers include, e.g., methyl methacrylate, ethyl methacrylate, propyl methacrylate and butyl methacrylate. In a particularly preferred embodiment, each of the third repeating units of the copolymer of the present invention is independently derived from a monomer selected from the group consisting of methyl methacrylate, n-butyl methacrylate and isobutyl methacrylate. Most preferably, each of the third repeating units is derived from methyl methacrylate. Use of methyl methacrylate as the (C 1 -C 4 )alkyl monomer of the present invention provides the greatest cost advantage due to the relatively low cost of that monomer relative to higher alkyl (meth)acrylate monomers. In a particularly preferred embodiment, the copolymer of the present invention includes about 43.9 mole percent first repeating units, each derived from lauryl methacrylate, about 14.7 mole percent second repeating units, each derived from cetyl-eicosyl methacrylate, and about 41.4 mole percent third repeating units, each derived from methyl methacrylate. In an alternative particularly preferred embodiment, the copolymer of the present invention includes about 35.2 mole percent first repeating units, each derived from lauryl methacrylate, about 22.5 mole percent second repeating units, each derived from cetyl-eicosyl methacrylate, and about 42.3 mole percent third repeating units, each derived from methyl methacrylate. The copolymers according to the present invention may, for example, be prepared from reaction mixture comprising a diluent, selected relative amounts of respective selected alkyl (meth)acrylate monomers, a polymerization initiator and a chain transfer agent. The reaction mixture preferably includes, from 15 to 400 parts by weight (pbw) diluent per 100 pbw total monomer charge and, more preferably, from 50 to 200 pbw diluent per 100 pbw total monomer charge. As used herein, "total monomer charge" means the combined amount of all monomers in the initial, i.e., unreacted, reaction mixture. In the method of the present invention, the total monomer charge includes from 15 mole percent to 67 mole percent, preferably from 25 mole percent to 60 mole percent, and most preferably from 25 mole percent to 40 mole percent, (C 8 -C 15 )alkyl methacrylate monomer. In the process, the monomer portion of the reaction mixture includes from 3 mole percent to 40 mole percent, preferably from 10 mole percent to 35 mole percent, and most preferably from 15 mole percent to 30 mole percent, (C 16 -C 24 )alkyl methacrylate monomer. In the process, the monomer portion of the reaction mixture includes from greater than 30 mole percent to 65 mole percent, preferably from 32 percent to 50 percent, and most preferably from 35 mole percent to 45 mole percent, (C 1 -C 4 )alkyl methacrylate monomer. Suitable polymerization initiators include initiators which disassociate upon heating to yield a free radical, e.g., peroxide compounds such as benzoic peroxide, t-butyl peroctoate, cumene hydroperoxide, and azo compounds such as azoisobutylnitrile, 2,2'-azo bis (2-methylbutanenitrile). T-butyl peroctoate is preferred as the polymerization initiator. The reaction mixture preferably includes from 0.25 pbw to 1.0 pbw initiator per 100 pbw total monomer charge and, more preferably, from 0.6 pbw to 0.8 pbw initiator per 100 pbw total monomer charge. Suitable chain transfer agents include those conventional in the art, e.g., dodecyl mercaptan or ethyl mercaptan. Dodecyl mercaptan is preferred as the chain transfer agent. The selection of the amount of chain transfer agent to be used is based on the desired molecular weight of the polymer being synthesized. The reaction mixture preferably includes from 0.5 pbw to 1.0 pbw chain transfer agent per 100 pbw total monomer charge, and more preferably includes from 0.6 pbw to 0.8 pbw chain transfer agent per 100 pbw total monomer charge. The diluent, used in the preparing the copolymer according to the present invention, may be any inert hydrocarbon and is preferably a hydrocarbon lubricating oil which is compatible with or identical to the lubricating oil in which the copolymer is preferably to be subsequently used. The reaction mixture is typically charged to a reaction vessel that is equipped with a stirrer, a thermometer and a reflux condenser and heated with stirring under a nitrogen blanket to a temperature from 90°C to 125°C. The batch is then typically maintained at a temperature from 90°C to 125°C for a period of 0.5 hours to 6 hours to carry out the copolymerization reaction. In a preferred embodiment, a portion, e.g., 25 to 60%, of the reaction mixture is initially charged to the reaction vessel and heated. The remaining portion of the reaction mixture is then metered into the reaction vessel with stirring while maintaining the temperature of the batch within the above described range for a period of 0.5 hours to 3 hours. In a preferred embodiment of the method, an additional amount of initiator, e.g., from 0.1 pbw to 0.5 pbw initiator per 100 pbw total monomer charge, is then typically charged to the reaction vessel and the batch is then typically maintained at a temperature within the above-specified range with stirring for a time period of 0.5 hours to 6 hours. A viscous solution of the copolymer of the present invention in the diluent is obtained as the product of the above-described method. A base oil may be treated with the copolymer of the present invention in a conventional manner, i.e., by adding the copolymer to the base oil to provide a lubricating oil composition having a desired pour point. A preferred embodiment of a lubricating oil includes from 0.05 pbw to 1.0 pbw copolymer per 100 pbw base oil. In a particularly preferred embodiment, the copolymer is added to the base oil in the form of a relatively concentrated solution of the copolymer in a diluent, e.g., a solution about 100 pbw of the copolymer dissolved in from 15 pbw to 600 pbw of the hydrocarbon diluent used in the above described polymerization process. A copolymer of the present invention may advantageously be used in combination with another pour point lowering copolymer, e.g., with a different embodiment of the copolymer of the present invention or with a copolymer selected from known poly(alkyl (meth)acrylate) copolymers, to provide pour point lowering copolymer blends, e.g., blends including from 50 pbw to 100 pbw of a copolymer according to one embodiment of the present invention per 100 pbw of a second pour point lowering copolymer. Such blends may be custom formulated for optimal performance in a particular base oil. A lubricating oil composition may include other additives in addition to the copolymer of the present invention, e.g., oxidation inhibitors such as dithiophosphate, detergent/corrosion inhibitors such as overbased metal sulfonates, antifoamants such as silicone polymers, and viscosity index improvers such as poly(alkyl (meth)acrylate) copolymers, olefin copolymers, hydrogenated styrene-butadiene copolymers. The following Examples are presented to illustrate various embodiments of the present invention. Examples C1 to C4 are Comparative Examples. In the Examples, 1 Poise = 0.1 Pa s, and 1 stoke = 1x10 -4 m 2 .s -1 Example 1 A monomer mix was prepared from 120 grams cetyl-eicosyl methacrylate (100% basis, 95.5% purity), 200 grams lauryl-myristyl methacrylate (100% basis, 97.5% purity), 80 grams methyl methacrylate (100% basis, 99.5% purity), 2.32 grams of a 50% solution of t-butyl peroctoate in mineral spirits , 2.80 grams dodecyl mercaptan, and 0.68 grams paraffinic base oil (100N oil). Part of the above monomer mix (30%) and 3.05 parts 100N oil were charged to a nitrogen flushed kettle fitted with a thermometer and a Thermowatch temperature controller ("Thermowatch" is a trademark), a water-cooled reflux condenser with nitrogen outlet, a stirrer, a nitrogen inlet, and an addition funnel to control the addition of the monomer mix. The contents of the kettle were heated to 105°C with provisions for cooling to maintain the batch temperature below 120°C, thereby controlling any exotherm. The batch was maintained at 105°C for about 5 minutes and then heated slowly to 115-120°C. The remainder of the monomer mix was added uniformly over a 60 minute period after the batch temperature reached 115°C. The temperature was maintained at 115-120°C for 30 minutes following completion of the monomer feed. At this point an initiator feed of 1.6 grams of a 50% solution of t-butyl peroctoate in mineral spirits and 33.6 grams 100N oil was added to the flask over 60 minutes at 115-120°C, after which the batch was held at the same temperature for an additional 30 minutes. The process yielded a viscous solution of a copolymer in the base oil. Monomer conversion to polymer was approximately 97%. The polymer so formed exhibited a number average molecular weight of 31,200 and a weight average molecular weight of 81,300, each measured by gel permeation chromatography. Approximately 39.92 parts 100N oil were then added to bring the batch to a final polymer solids content of 64%. Examples 2 to 19 and C1 to C4 The copolymers of Examples 2 to 19 and C1 to C4 were each made according to the process described above in Example 1, except that different amounts of the respective comonomers were used. Table 1 below sets forth the relative amounts (mole %) of the respective comonomers, i.e., cetyl-eicosyl methacrylate (CEMA), laurylmyristyl methacrylate (LMA), methyl methacrylate (MMA), butylmethacrylate (BMA), isodecyl methacrylate (IDMA), for each of those Examples. EXAMPLE NUMBER CEMA/LMA/MMA/BMA/IDMA (mole %) 2 19.8/56.6/33.6/0/0 3 18/36.4/45.6/0/0 4 17.4/33.5/49.1/0/0 5 16.4/28.0/55.6/0/0 6 11.3/33.9/54.8/0/0 7 16.7/50/33.3/0/0 8 14.7/43.9/41.4/0/0 9 19.8/46.6/33.6/0/0 10 18.6/39.6/41.8/0/0 11 25.7/40.2/34.1/0/0 12 22.5/35.2/42.5/0/0 13 30.6/34.9/34.5/0/0 14 28.6/28.4/43/0/0 15 7.2/52.2/40.6/0/0 16 21.3/0/39.9/0/38.8 17 12.2/46.7/41.1/0/0 18 14.1/42.2/0/43.6/0 19 15.4/46.0/0/38.6/0 C1 25.1/74.9/0/0/0 C2 39/61/0/0/0 C3 23/67/13/0/0 C4 21.3/54.6/24.1/0/0 Examples 20A to 20GG Each of Examples 20A to 20T and 20Z to 20 BB were made by preparing a solution of 0.15 wt % (polymer solids) of a respective one of the copolymers of Examples 1 - 6, Examples 15-19, or C1, C3, C4 in a base oil. Each of Examples 20U to 20Y and 20CC to 20 GG were made by preparing a solution of 0.19 wt% (polymer solids) of a respective one of the copolymers of Examples 15-19 in a base oil. The pour point of each Example so formed was measured by both ASTM D- 97-87 and "Cycle C" test methods. The sonic shear index (SSI) of each of the Examples was measured by the method of ASTM D 2603-91 following 12.5 minutes sonic shearing. The copolymer (Example No.), the lubricating oil base stock (A=Exxon 100N (ASTM pour point=-21°C), B=Exxon 600N, C=Quaker State Congo 125N, D=Sentry 70 (ASTM pour point = -15°C)), the ASTM pour point (°C) and the Cycle C pour point (°C) are each given below in Table 2 for each of Examples 20A to 20GG. Sonic Shear Index (SSI) values are also given for Examples 20A-20I, 20O-20T and 20Z-20BB. EXAMPLE NO. ADDITIVE (EX. NO.) BASE STOCK ASTM POUR POINT (°C) CYCLE C POUR POINT (°C) SSI 20A C1 A -39 -33 16.1 20B C3 A -45 F-39 19.2 20C C4 A -39 F-39 22.9 20D 2 A -39 F-39 24.9 20E 1 A -39 F-39 15.3 20F 3 A -39 F-39 17.6 20G 4 A -39 -39 16 20H 5 A -36 F-39 14.2 20I 6 A -39 -39 16.0 20J 15 A -27 -33 - 20K 16 A -27 -27 - 20L 17 A -33 -36 - 20M 18 A -33 F-39 - 20N 19 A -36 F-39 - 20O C1 B -20 -24 16.1 20P 2 B -21 -24 24.9 20Q 1 B -24 -24 15.3 20R C1 C -33 -33 16.1 20S 2 C -30 -33 24.9 20T 1 C -36 -33 15.3 20U 15 C -33 -33 - 20V 16 C -21 -24 - 20W 17 C -36 -30 - 20X 18 C -36 -33 - 20Y 19 C -36 -33 - 20Z C1 D -27 -30 16.1 20AA 2 D -24 -30 24.9 20BB 1 D -24 -30 19.2 20CC 15 D -12 -12 - 20DD 16 D -13 -12 - 20EE 17 D -15 -12 - 20FF 18 D -15 -12 - 20GG 19 D -12 -12 - The viscosity of each of Examples 20A, 20E, 20O 20Q, 20R, 20T, 20Z and 20BB was measured at -15, -20, -25, -30, and -35°C using a mini rotary viscometer (MRV) according to the method of ASTM D 4684-89. Results are set forth below in Table 3 as apparent viscosity (0.1 Pa·s, Poise) at each temperature for each of those Examples. A Borderline Pumping Temperature (BPT) is also set forth for each Example. The notation "TFTM" (too fluid to measure) is used in Table 3 to indicate that the viscosity of a particular sample was too low to measure in using the MRV at the indicated temperature EX. NO. -15°C -20°C -25°C -30°C -35°C BPT 20A - - TFTM 28.3 92.3 >-35 20E - - TFTM 27.6 82.8 >-35 20O 119 280 1168 - - -19.8 20Q 125 269 1057 - - -19.9 20R - - 29.0 69.7 182 -36.9 20T - - 17.7 63.1 200 -35.8 20Z 136 276 963 - - -19.8 20BB 112 235 778 - - -20.8 Examples 21 and C22 Two series of samples, 21A to 21H and C22A to C22G, were made by dissolving the respective copolymers of Examples 1 and C1 in a base oil (Quaker State 125N) to provide formulations having the compositions given in Table 4 (Samples 21A to 21H use the copolymer of Example 1, and Sample C22A to C22G use the copolymer of Example C1). The ASTM D 97-87 pour point (°C) and Cycle C pour point (°C) were each measured for each sample and are given in Table 4. EXAMPLE NO. WT % POLYMER SOLIDS ASTM POUR POINT (°C) CYCLE C POUR POINT (°C) Base Stock 0.00 -12 -12 21A 0.16 -36 -33 21B 0.12 -36 -33 21C 0.11 -36 -33 21D 0.08 -36 -30 21E 0.053 -30 -30 21F 0.04 -27 -30 21G 0.32 -30 -30 21H 0.026 -27 -33 C22A 0.15 -36 -33 C22B 0.112 -36 -30 C22C 0.10 -36 -30 C22D 0.075 -33 -30 C22E 0.05 -33 -30 C22F 0.038 -33 -33 C22G 0.025 -33 -27 Examples 23A to 23 J The copolymers of Examples C1, C2 and 9 to 16 were added to an SAE 15W-40 lubricating oil (0.15 wt% copolymer solids in Imperial PL23720-1 oil). The shear stability of each of the Examples was measured by ASTM D 2603-91. The viscosity of each of the samples was measured by ASTM D 4684-89 at -20°C and -25°C using a mini rotary viscometer. The pour point of each of the samples was measured according to the Cycle C test method. The shear stability following 12.5 minute sonic shear (% SLDTP), the percent bulk (weight %), the Cycle C pour point (°C) and the D 4684-89 apparent viscosity (0.1 Pa·s, Poise) at -20°C and -25°C is forth below in Table 4 for each of the Examples. EX. NO. ADDITIVE EX. NO. % SLDTP % BULK CYCLE C POUR POINT Viscosity (Poise) -20°C -25°C 23A C1 16.1 0.260 -18 9036 Solid 23B 9 16.6 0.258 -30 3133 Solid 23C 10 12.3 0.260 -30 154 427 23D 11 13.9 0.258 -36 162 458 23E 12 17.2 0.258 -36 142 411 23F C2 15.3 0.254 -36 156 430 23G 13 13.3 0.179 -36 161 432 23H 14 16.0 0.344 -36 145 373 23I 15 16.6 0.258 -36 154 403 23J 16 12.0 0.258 -36 159 410 Examples C24A, C24B and 25A to 25C A group of SAE 10W-30 lubricating oils, Examples C24A, C24B and 25A to 25C, were formulated by combining a base oil with a viscosity index improver, a pour point depressant, an ashless dispersant, and a detergent/inhibitor package ("DI package") in the amounts set forth below in Table 6 ( amounts are given as weight percents). C24A C24B 25A 25B 25C Viscosity Index Improver (Exxon ECA 13111) 7.0 7.0 7.0 7.0 7.0 Pour point Depressant Example C3 --- 0.2 --- --- --- Example C1 --- --- 0.2 --- --- Example 1 --- --- --- 0.2 --- Example 4 --- --- --- --- 0.2 Ashless Dispersant (Amoco 9250) 2.0 2.0 2.0 2.0 2.0 DI Package (Amoco PC800-4) 10.45 10.45 10.45 10.45 10.45 Base Stock (Pennzoil HF 150N) 80.55 80.35 80.35 80.35 80.35 The kinematic viscosity of each of Examples C24A, C24B and 25A to 25C was measured at 100°C by the method of ASTM D445-88 and at -20°C by the method of ASTM D5293-92. The pour point of each of the Examples was measured by the methods of ASTM D 97-87 and Cycle "C". The viscosity and borderline pumping temperature of each of the Examples was measured by ASTM D4684-89 using a mini rotary viscometer (MRV). Results are set forth in Table 7 as: the ASTM D445 apparent viscosity (100°C Vis), expressed in mm 2 ·s -1 (centi Stokes (cSt)); the ASTM D5293 apparent viscosity (CCS Vis, - 20°C), expressed in 0.1 Pa·s (centi Poise (cP)); the ASTM and Cycle C Pour points, each expressed in degrees centigrade (°C); the ASTM D 4684 apparent viscosity, (TP-1 MRV), expressed in 0.1 Pa·s, (Poise (P)); the ASTM D3829 apparent viscosity, (MRV), expressed in 0.1 Pa·s Poise (P); and the borderline pumping temperature, (TP-1 MRV BPT and MRV BPT), expressed in degrees centigrade (°C). EX. NO. C24A C24B 25A 25B 25C 100°C Vis (cSt) 11.16 11.23 11.11 11.22 11.19 CCS Vis., -20°C (cP) 3100 2860 3060 2910 2840 ASTM Pour Point, (°C) -18 -33 -36 -30 -30 Cycle C Pour Point (°C) -33 -33 -33 -33 -30 TP-1 MRV (P) -20°C 35.2 32.6 16.7 34.0 34.7 TP-1 MRV (P) -25°C 81.9 69.9 77.1 77.6 74.6 TP-1 MRV (P) -30°C 205 189 197 210 201 TP-1 MRV (P) -35°C 720 589 620 680 618 TP-1 MRV BPT (°C) -31.6 -32.2 -32.0 -31.7 -32.0 MRV (P)-20°C 39.7 31.4 36.2 32.8 33.6 MRV (P)-25°C 105 70.5 73.6 77.8 74.6 MRV (P)-30°C 544 182 186 207 190 MRV (P)-35°C --- 521 560 608 533 MRV BPT (°C) -28.4 -32.6 -32.3 -31.9 -32.4 Example 26 A group of lubricating oil samples, Examples 26A to 26O, were formulated by adding a pour point lowering copolymer or a 50/50 wt % mixture of two different pour point lowering copolymers to an SAE 15W-40 lubricating oil (Imperial PL 23720-1) at a level of 0.08 weight % copolymer solids. The pour point of each Example was measured by the "Cycle C" test method and the apparent viscosity of each of the Examples was measured by the method of ASTM D 4684-89 at -20°C and -25°C using a mini-rotary viscometer. The pour point lowering copolymers are identified (EX. No.) and the Cycle C pour point (°C) and the apparent viscosity 0.1 Pa·s (Poise) at -20°C and -25°C are given below in Table 10 for each of Examples 26A to 26O. EX. No. ADDITIVES (EX. NO.) CYCLE C POUR POINT (°C) Viscosity (Poise) -20°C -25°C 26A C1 -12 Solid Solid 26B C2 -33 162 436 26C C1/C2 -36 157 415 26D 7/11 -36 99.8 265 26E 18/12 F-39 106 253 26F 7/C2 -36 109 288 26G 8/C2 -33 103 287 26H 11/C1 F-39 106 271 26I 12/C1 F-39 109 284 26J 9/13 -36 98.1 230 26K 10/14 -30 107 265 26L 9/C2 -33 101 254 26M 10/C2 -36 111 267 26N 13/C1 -33 162 408 26O 14/C1 -33 112 257 The pour point lowering copolymer of the present invention includes a large relative amount of repeating units derived from lower alkyl (meth)acrylate monomers, i.e., from greater than 30 mole percent to about 65 mole percent monomeric units derived from a (C 1 -C 4 )alkyl (meth)acrylate monomer, most preferably methyl methacrylate. The copolymer provides high performance as a pour point lowering additive in a wide range of base oils at a reduced cost relative to pour point lowering copolymers that include a smaller relative amount of lower, i.e., C 1 -C 4 , alkyl (meth)acrylate comonomeric units and a larger relative amount of higher, i.e., C 8 -C 24 , alkyl (meth)acrylate comonomeric units.

Claims: A random copolymer, which comprises: i) from 15 mole percent to 67 mole percent first repeating units, each of said first repeating units having the structural formula: wherein each occurrence of R 1 is independently H or methyl, and each occurrence of R 2 is independently selected from the group consisting of (C 8 -C 15 )alkyl; ii) from 3 mole percent to 40 mole percent second repeating units, each of said second repeating units having the structural formula: wherein each occurrence of R 3 is independently H or methyl, and each occurrence of R 4 is independently selected from the group consisting of (C 16 -C 24 ) alkyl; and iii) from greater than 30 mole percent to 65 mole percent third repeating units, each of said third repeating units having the structural formula: wherein each occurrence of R 5 is independently H or methyl, and each occurrence of R 6 is independently selected from the group consisting of (C 1 -C 4 )alkyl. A copolymer as claimed in claim 1, wherein the copolymer has a number average molecular weight from 20,000 to 80,000, preferably from 25,000 to 70,000, and more preferably from 28,000 to 60,000. A copolymer as claimed in claim 1, wherein the copolymer has a weight average molecular weight from 50,000 to 200,000, preferably from 50,000 to 175,000, and more preferably from 50,000 to 100,000. A copolymer as claimed in any preceding claim, wherein the copolymer comprises from 25 mole percent to 60 mole percent, preferably from 25 mole percent to 40 mole percent, of said first repeating units. A copolymer as claimed in any preceding claim, wherein the copolymer comprises from 10 mole percent to 35 mole percent, preferably from 15 mole percent to 30 mole percent, of said second repeating units. A copolymer as claimed in any preceding claim, wherein the copolymer comprises from 32 mole percent to 50 mole percent, preferably from 35 mole percent to 45 mole percent, of said third repeating units. A copolymer as claimed in any preceding claim, wherein: a) R 1 , R 3 and R 5 are each methyl; and/or b) R 2 is selected from the group consisting of isodecyl, lauryl, tridecyl, myristyl, pentadecyl and mixtures thereof; and/or c) R 4 is selected from the group consisting of stearyl, cetyl, eicosyl and mixtures thereof, preferably R 2 is selected from the group consisting of lauryl, tridecyl, myristyl, pentadecyl and mixtures thereof; and/or d) R 6 is selected from the group consisting of methyl, n-butyl, isobutyl and mixtures thereof, preferably methyl. A copolymer as claimed in any preceding claim, wherein: a) each of the first repeating units is independently derived from a (C 8 -C 15 )alkyl methacrylate monomer, and preferably each of the first repeating units is independently derived from a monomer selected from isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, myristyl methacrylate and pentadecyl methacrylate; and/or b) each of the second repeating units is independently derived from a (C 16 -C 24 )alkyl methacrylate monomer, and preferably each of the second repeating units is derived from a monomer selected from stearyl methacrylate, cetyl methacrylate and eicosyl methacrylate; and/or c) each of the third repeating units is independently derived from a (C 1 -C 4 )alkyl methacrylate monomer, and preferably each of the third repeating units is derived from a monomer selected from methyl methacrylate, n-butyl methacrylate and isobutyl methacrylate. A copolymer as claimed in any of claims 1 to 8, wherein each of the third repeating units is derived from methyl methacrylate. A copolymer as claimed in any of claims 1 to 6, which comprises: (a) about 43.9 mole percent first repeating units derived from lauryl methacrylate, about 14.7 mole percent second repeating units derived from cetyl-eicosyl methacrylate, and about 41.4 mole percent third repeating units derived from methyl methacrylate; or (b) about 35.2 mole percent first repeating units derived from lauryl methacrylate, about 22.5 mole percent second repeating units derived from cetyl-eicosyl methacrylate, and about 42.3 mole percent third repeating units derived from methyl methacrylate. A method for making a pour point lowering copolymer as claimed in any of claims 1 to 10, which comprises: copolymerizing a mixture of monomers in a hydrocarbon diluent, said mixture of monomers comprising: from 15 mole percent to 67 percent of one or more (C 8 -C 15 ) alkyl (meth)acrylate monomer, from 3 mole percent to 40 mole percent of one or more (C 16 -C 24 ) alkyl (meth)acrylate monomer; and from greater than 30 mole percent to 65 mole percent of one or more (C 1 -C 4 )alkyl (meth)acrylate monomer. A pour point depressant composition which comprises about 100 parts by weight of a copolymer as claimed in any of claims 1 to 10, or of a copolymer prepared by a method as claimed in claim 11, and from 15 to 600 parts by weight of a hydrocarbon diluent. A lubricating oil composition which comprises a lubricating oil base stock and from 0.05 weight percent to 1.0 weight percent based on the weight of the lubricating oil base stock, of a copolymer as claimed in any of claims 1 to 10, or of a copolymer prepared by a method as claimed in claim 11. A method for lowering the pour point of a lubricating oil, comprising: adding to the oil from 0.05 weight percent to 1.0 weight percent, based on the weight of the lubricating oil, of a copolymer as claimed in any of claims 1 to 10, or of a copolymer prepared by a method as claimed in claim 11.

Inventors: GORE ROBERT HOWARD, O'MARA JAMES HERBERT, GORE, ROBERT HOWARD, O'MARA, JAMES HERBERT
Applicants: ROEHM ROHMAX HOLDING GMBH
Application year: 1994
Main classification: C10M145
IPC codes: C08F255, C08F220, C10M145, C10N30